Electrolytic process for reducing sugars



Jan. 11, S1949.` H. J. CREIGHTQN ET AL 2,458,895

`ELECTROLYTIC PROCESSFOR REDUGING SUGARS mw ATTOR N E Jan- 11, 1949- H.J. cRElGHToN ET Al. 2,458,895

ELECTROLYTIG PROCESS FOR REDUCING SUGARS Filed May 21, 1943 2Sheets-Sheet 2 ATTORN Y Patented `an. 11, 1949 ELECTROLYTIC PROCESS FORREDUCING .SUGARS Henry Jermain Y Creighton, Swarthmore, and Ralph A.Hales, Tamaqua, Pa., assignors to Atlas Powder Company, Wilmington,Del., a

corporation of Delaware Application May 21, 1943, serial No. 487,870

The present invention relates to an improved process forelectrolytically reducing sugars to polyhydric alcohols.

An object of the invention is to improve the eiciency oi theelectrolytic reduction process by reducing greatly the time necessary tocomplete the reduction.

Another object is to increase the production of present electrolyticcell equipment by shortening the time of reduction.

A particular object is to improve the efficiency of the processforelectrolytically reducing glucose to one ormore polyhydric alcohols.

The reduction or hydrogenation of reducible sugars by the electrolyticprocess is a known and commercially practiced operation. Broadly theprocess involves the use of an electrolytic diaphragm cell providingseparated anode and cathode compartments. The anolyte isa solution of anelectrolyte, preferably sulfuric acid, in water. The catholyte is asolution of the sugar to be reduced together with a suitable'electrolyte in Water. In the catholyte the electrolyte is preferably analkali metal compound, like sodium sulfate, .to which is frequentlyadded an alkali hydroxide. The anode in the process is an Velectricallyconductive material resistant to thecorrosive'action of the anolyte. Incommercial practicevthe cathode is a rigid plate'of lead or zinc. Thecathode may also be made ofvany rigid material and covered with a layerof lead or Zinc. Lead cathodes'are amalgamatecl before use.v Zinccathodes are used either amalgamated or unamalgam'ated. When the anodeand cathode are connected to a source of direct current nascent hydrogenis formed at the cathode and sugar in the catholyte solution is therebyreduced to one or more polyhydric alcohols.

B y means of this electrolytic process a series of polyhydric alcoholscan be made from reducible sugars. Conditions can be selected to producethe polyhydric alcohol which directly corresponds to the sugar, or toproduce mixtures of polyhydric alcohols some of which do not corresponddirectly to the sugar. Thus, from glucose can be made sorbitolwhich isthe corresponding hexitol, or a mixture of mannitol and sorbitol can bemade, or theproduct can be composed of mannitol, sorbitol and otherpolyhydric alcohols such as hexane pentols. The last two types ofproducts 4 Claims. (Cl. 2044-77) are produced when the catholytesolution is maintained at a` relatively high alkalinity while the firsttype is made at very low alkalinity or with the catholyte in a neutralor acid condition.

This process is more completely described in y the patentto H, J.Creighton, No, 1,990,582; and

in the patents to R. A. Hales, Nos. 2,289,189, 2,289,190, 2,300,218, and2,303,210. In commercial practice the catholyte is circulated throughthe cathodecompartmentiand through a heat exchanger and receiver, asdescribed in the patent to H. J'. Creighton, No. 1,990,582, so that thetemperatureand rcomposition of. the catholyte can be controlledthroughout the operation. y

While `the above-described process has been commercially successful ithas been slow in operation, requiring reduction times in theneighborhood of 200 hours for completion of a large scale reduction.This long period of operation has Vthe effect of requiring large cellcapacity for a given volunef 'of production.

Thepresent `invention resides ink an improvementof the' electrolyticprocess which greatly increases"- the rate of reduction therebyincreasing the productivity ofcell equipment. Operatinginaccordance'with theinvention results in increasing up to ten-iold'ormore the rate of reduction of the process. Another advantage of thepresent process resides in operating economies made possible intemperature control by virtue of the fact that the process is conductedat a higher temperature than the known process.

Broadly the invention employs a higher operating catholyte temperaturethanthat previously employed, plus a higher cathode current density thanthat previously employed, the temperature and current density valuesbeing correlated according to a definite plan which takes into accounttwo other process variables, namely, the

concentration of sugarin the catholyteand theV relation of the area ofthe cathode to the volume of the catholyte. f f

' In` the prior practiceof the electrolytic process, the catholyte wasmaintained at a temperature of about' 68or 69 Fahrenheit vand thecurrent densityl at the cathodev was about 1 ampere or less per squarevdecimeter of cathode surface. Higher temperatures Were tried and foundunsatisfactory. in the priorfprocess because they impaired.` the quality-oiz' the product through darkening lthe color, and producing organicacids in objectionable quantities. Raising the temperature alone did notimprove the rate of reduction. A further eiect of raising temperaturealone was to give products of different composition than the normalprocess. It had also been attempted to increase the rate of reduction byraising the current density at the cathode without making any change inthe catholyte temperature. The result of this attempt was that noincrease in the rate of reduction occurred and the current efficiency ofthe process dropped off sharply,

In the process'ofthel invention the catholyte is maintained at atemperature of at least '72,"

Fahrenheit and not over 135 Fahrenheit. Raising the temperature alone,vhowever, produces only the disadvantages just discussed. We have foundit to be possible to compensate for 4this higher operating temperatureby"increasing-the current density at the cathode tdafvalue `ofl'l ampereor higher per square'decimeter of cathode surface. The upper limit ofcurrent density is a practical one because extremely Thigh currentdensities involve excessive power costs. In general current densitiesshould not exceed'lO amperes per square decimeter of cathode surface forthis reason. It does not suice to select-any two valuesl of-temperatureand current density at random but these variables -must be correlated tocompensate for one another. `We -have further found that the particularvalues of teme perature and current-,density to be used'depends in agiven case on Athe concentration of sugar in thecatholyte-and-alsoon*the ratio of cathode area to catholytey volume.

`For convenience in presentation, vthe relationship of these fouroperating variables has been broken down into temperature as one-elementand 'the expression grams vinitial vsugar per ampere as theotherelement. The expression grams initial sugar per ampere is derivedbyfactoring the fraction c., A exon wherein, Cu is the number ofigr-amsofvsugar perv literof catholyte, Ris the ratio =ofthe.cathode area insquare decimeters Ato the volumevof the catholyte in liters,A andCD isthe ,current density at'the cathode-in amperes per square decimeter-ofcathode surface. Supplyingthe values of the symbols inthe fractiongives grams sugar liter amperes dm.2 liter which on factoring becomesgrams sugar amperes v` the cell will retain aqueous solutions withoutleakage and resist the corrosive actions of strong @electrolytesDisposed Within the body of the {ficell are diaphragme 26, which alsoare of box- Referring'now to .the` accompanying drawings l wherein like.numerals .designate corresponding Dalits,

`iFigure lisa diagrammatic representationfof -an like structure, open atthe top. The diaphragms are made of "semiepermeable material so as to pm,prevent .liquids on opposite sides thereof from ..,'fre,ely,intermixingbut offering little resistance to the passage of charged ions throughthe walls. .Atsuitable material for the construction of the diaphragmsis sintered aluminum oxide such as the material sold under thetrade-mark Alundum. In the form of cell illustrated in Figure i;twodiaphragms lare employed. Suspended in the diaphragm-boxes 2-6 arethe ano des2l,'which are preferably made of chemical ',lead, Aalthoughother current conductive, corrosionresistantmaterials can tbe used.lOutside .of the diaphragm boxes "26 and iintthe main body-'of Athe'cell"25 cathodes 28 areypositioned. The `cathodes are rigid k'plates`with metallic surfaces lsuch `vas lead orzinc. The cathodescan be madeof solid metal or of suitable base material-coveredfbyya 'layer of suchmetal. Whenthe cathode surface is lead, itis amalgamated by dippingn orrubbing'with mercury or dipping in mercurio nitrate solution beforeusing. `Wherethefsurface is of zinc, 'the cathode Acan; be usedl eitherwith or withoutamalgarnation. 'jIt .vs/ill, thus,'be seen lthatjthe cellbody 2 5 is divided bymeans ofthe diaphragms 2 6 "into -anode andcathode .compartments "The anode compartments are provided with. theanolyte'j vwhich is .an aqueous solution .of a current carryingelectrolyte, preferably sulphuric acid.

he -,cathode `compartment, which is actually 'the body of the celloutside the Vdiaphragms 26, is provided with the catholyte 29, which isan aqueoussolutionl of the sugar to be reduced.A and a current carryingalkali metal electrolyte.

A'Ilxeanodes'l and cathodes '28 of 'the cell are connectedrespectivelyto the positiveand negative terminals of a source of direct current.When the-solutions are placed withinthe cell and anelectr-ic current is,passed between the anodes andcathodes, the sugarin thevcatholyte isreduced .or rhydrogenated to .form `the ,polyhydric alcoholproduct.

L'Iheconcentration of sugar will depend upon its.solubnitymmeramente2.9. In .the ease ,of glucose, the preferred,concentrationfis between 2.0.and.'700.grams,per liter. The preferred sugar isi-,.glucose, becauseof-.the valuable products .,obtainedfrom-it, although other reduciblemonosaccharides .such :as fructose, Vmannose, -the .mixture of tglucoseand fructose obtained .by theinversion of 4s ucroseLthe.mixture ofglucose and4 galactose obtained by the inversion of lactose,andpentoses, andreducible disaccharides, ,such .as .-lactose, canbei-used.

{Ifhe .-ratio of cathode area to catholytefvolume is .-Lsusceptible ofxwide yvariation but forg practical purposesgthe range of,.0.25to {10squarefdeoimeters of cathode surfacep'erliter of catholyte is preferred.This ratio can be controlled at a selected upper surface of thecatholyte to prevent contact with air. Suitable means for this purposeare disclosed in the application of K. R. Brown, Serial Number 458,820,filed September 18, 1942,'"now n abandoned.

The temperature of the catholyte may be adjusted initially by heating orcooling, as required,

before starting the reduction. The reduction process results in thegeneration of heat in the solutions and during the operation of a cellthe catholyte temperature is kept at the desired value by cooling. Thetemperature control may be accomplished by conventional means such asim'- mersing the cell in a bath of liquid, by owing a liquid throughcoils immersed in the cell solutions7 by circulating the cell 'solutionsthrough external heat exchangers, etc. In large scale installations itis customary to employ external heat exchangers for temperature control,as described for example in the patent to H. J. Creighton', No.1,990,582. [l

Referring now to Figure 3, the graph is of the semi-logarithmic typewith temperature in degrees 'Fahrenheit represented arithmetically asthe abscissa and grams initial sugar per ampere represented`logarithmically as` ordinate. The area bounded bythe line ABCDEAcontains the pointswhich represent the range of operativeratios oftemperature to grams initial sugar per ampere when current densities ofat least 1.1 amperes per square decimeter of cathode surface are used.For a given set of conditions of sugar,

catholyte alkalinity (or acidity), and cathode material, substantiallythe same product can be made at the ratios of temperature to gramsinitial 3' sugar per ampere which lie on lines parallel to the line BC.For example, the line FG represents ratios of temperature to gramsinitial sugar per ampere for making Aa high vpurity sorbitol from`glucose with anamalgamated zinc cathodeand with a catholyte containingfrom 0 to 2.0 grams NaOH per liter.- Similarly, the lineI-II representsvratios .for making mannitol anda noncrystallizing sorbitolsyrupiromglucose with an amalgamated i lead cathode and Witha catholytecontaining.

from l0 to20 grams NaOI-I per liter.A

two reductions employing ratios lying on diierent linesparallel to BC,that which is farther from BC 'will produce a product higher inpolyhydric alcohol obtainable directly by hydrogenating the carbonylgroup ofthe selected sugar to a carbinol group. Where the selectedsugars are hexoses the directly obtainable polyhydric alcohols arehexahydric alcohols also called hexitols. An

aldo-hrexose yields only one hexitol by direct hydrogenfation undernon-isomerizing kconditions while a keto-hexose yields two hex-itolsbydirectIv vwFor the same sugar, catholyte alkalinityI (or acidity) andcathode` material, Variations in theV 6. hydrogenation.`lFor'convenience in description the polyhydric alcohols obtainable bydirect reduction 'of a sugar are referred to as the specic hydrogenationproducts of that sugar to distinguish from so-called non-specic productswhich are polyhydric. alcohols obtainable only by more complex reactionswhich may include, for example, isomerization of the sugar,

hydrogenation of carbinol groups to hydrocarbon groups, and carbon chaincracking. From glucose, for example, the reduction using 4a ratio yfalling on the line farther from BC Will give a product containing moresorbitol than an othery .wise identical reduction using a ratio fallingon the line nearerfto BC. The reduction employing a ratio falling on theline nearer to BC will give relatively moreof the nonspeciiichydrogenation products, which from glucose are mannitol and non-hexitolcompounds chiefly hexane pentols. These effects Will become moreapparent from a consideration of the examples.

ATheinvention provides a range of novel operating conditions throughoutwhich the advantages of faster rate of reduction and improved eiciencyin temperature control are obtained. Furthermore, the invention providesa series of operating ratios of temperature to grams initial sugar perampere for making products of like composition at xed conditions ofsugar, catholyte alkalinity (or acidity) and cathode material.

For convenience in presentation and for better comparison the followingexamples are tabulated.

'Glucose solutions Were reduced in each example,

75 g. of sodium sulfate per liter being added to carry the current. AnAlundum diaphragm separated the catholyte from the anolyte which was adilute aqueous solution of sulfuric acid.

The tabulated items are:

Ratto-' The ratio of the surface area of the cathode, in squaredecimeters, to the volume of the cathode, in liters.

C. D.-The current density in amperes per square decimeter of cathodearea.

Temp-The temperature in degrees Fahrenheit of the catholyte duringreduction.

P. N.-The pyridine number of the product.

` This value is a measure of the sorbitol content is a measure of thetime efficiency of the reduction. The gures are computed with referenceto 99% sugar.'l reduction except where otherwise noted.

@wmp- Grams initial sugar per ampere, the value of the expression Gramsyinitial sugar per liter of catholyte Ratio XC.1D.

Examples. 1 to' 10 inclusive employed amalgamated ylead cathodes, floatson the catholyte in the receiver, and an alkali concentration initially10 g. NaOH .per liter which Was allowed to increase :togv 20:g."d'uring`the reduction and Was 1f maintained thereafter at the*I latter-1value1-z by:` neutralization asrequiredz.

The following table givesexamples of reduc tions` :according to theinventiom` I n: Examples. 1- andV 2 the catholyte contained initially500 g. glucose per liter While in vtheotherf. examples the tions of.theiother `variable:ffactonszoif. the-faccinea tiem.

time?l following tahteff. the-2 threei' reductions' according? tosth'e?inventiom .weref alla* carried: ont

with; catholytesr. atiY an' initials: concentra-tion`4 of;A

325: e. .glucoseoperr liter: The.;- threeif examplesa catholytecontained-initially. 325; g.: glucose per"y (11; ,12. and 13) werereductionsin'iwhichranvinieliter. l tial alkalinityof 5.0 g. NaOH perlitemofcatho'- Table-I Example Ratio C, D. Temp. PxN. lMan Yieldg./dm.*/hr. gjamp 1.21 4.0 si 40.55 1714# ses 4.75 10aA 1.21 10.0 10018; 14.9.; 90.5 13.2; f ,i A411.13.

1.21` 4.o se 52 17.6 l 93.1 5.2i'.- Y 01.2

1.121 2.0 75 4a zozo 9120 2.40 `134.

2.0` 2.o s1. 54.A 17.11` 011.13 2.60 81.3

2.0 6.oV 11o 12.. 1 .5- Saiz-g 9.43 27.1.

For comparison with theexamples in..Tab-le-I which are in accordancewiththe presentimien tion.. the following-table givestwo.examplesoilreductions atvaluesof temperature and-.currentdensity outside of thevalues contemplated byithis lyte was allowedatoincrease to...10.'0. gperv liter. at which. valueet .was kept.. b'yf neutralization rasrequired... Examples.,11..and.; 12.- were conducted:- withamalgamatedzinc cathodes:while:ineExamV ple .131 anam-alganrated .leadcathode was used..

invention. Example 95 had acatholyteconcentration of 5602-g.. glucoseper liter-ai'id'th'ecatho` lyte in Example 10 hadf 325g. glucosecperliter. These reductions were both conducted at thesarne Notable.: in:the foregoing:A examplesf. are -.th"e.. sharp. riseffinzxfate'ofireductiom andE thewra'dicali change :iny the. composition :of'ftheprodncti oExe Y ampleI2:asecomparedztoExamplel1I: These two alkalinityas the examples in Tablel I'. 40examples-awei:efsi'rnilar;inallirespects:excepixtelri Table II t YExample Ratio C. D. Temp. I. N. Man. Yield. gJdm/hr.V g-Jamp.

In Example 9 both temperaturefandcurrent f density were below the valuesused in vfollowingthe present invention. Therate 4of reductionof sugaris markedly lower than 'thef'rates-in any of' the examples in Table I.For instanceExample 2 shows :a rate of reduction over eight times-thatof Example 9. Note the increase in the'rate -of reduction obtained evenloy` concurrently raising-f' the temperaturer to 75 F. and thecurerntdensity to 2.0 as in Example Las compared to the rate obtained at 69 F. and1.0 ampereein-Example 9. Example 10 shows a decreasefwinethew rate ofreduction compared to ExampleuQ'when the temperature is raised to 8P' FLand the current density held at 1.0 ampere. the 0 P. N. and 1.2%mannitol ofthe productof Example 10. I

Examples 1 and 6 following theA invention and Example 9 following theprevious practice all produced substantially the same product, as far assorbitol (determined as P. N.) and mannitol are concerned,1 although thetemperatures. and current densities. of these` examplesanwererwidely"dierent. These examples'are `illustrativef-of'ithef.k variation of.temperature and current-density tot produce. similary products. under:various rcaomiiI Noteazaflsofv peratnrei: Iii-Example.` 11 thetemperature-was Qilf'fli; whiiefin Example-12 the-terrip'erature"was1.00%?? The; dlii'lererireein--methodes` is *strikingly*showmimExampl'es `12and^I` i otherwisesimilar;l where 'hef change from==air amalgamatedv zincvv sariify'show"complete` absence. of' sorbitollit' does'- shovwvery low sorb'itol content... Example-13"ex liiltsagreat increaseinheth .scribi-tol and. man.-

. nitoloonterit oil. theprbduct...

` Table.. gives further .examp1es--ofreductionsY' ing. accordancewitl-rf the.V invention,- inwV which z a'.catholyteccont-ainingi:325i-g. gilucosefrfper .literf was reducerlnat,an 'alleaiimityfinitiailyzeg: NaQHrip-er: litertwhiclmwasnaliowedrto'frise to:1.51g;.per liter-'imA the.` course.: ofreduction: ande was keptf between these vval-'frese105V`neutralizationw-as. required; Inr- Examplesee 144 to; 17 amalgamated'zi'noj-l -catl'iodesf' were used*lw11il irrExample-f lli-"ankama-lga-mat'edl' learlcathodewaslused Table IV Example Ratio C. D. Temp.P. N. Man. Yield gJdm/hr. gJamp 2.0 4.0 si 76 0 93.3 ls 40.6

Examples 14 and 17 gave a product with sub- The improvement in the rateof reduction of stantially the same P. N. and mannitol content Exampley.as compared with Example 21 is atalthough Example 14 was run with acatholyte tributable to the increase of'temperature from temperature of81 F. and -at a current density 68 F., in Example 21, to 90 F., inExample 20, of 4 amperes while Example 17 was run at 90 F. V and to thesimultaneous increase in current denand 6 amperes. However, Example 17shows a l" sity from 1.0 in Example 21,' to 2.6 to 2.7 in Exrate ofreduction over higher than Example ample 20. f 14. Example 18 shows arelatively low rate of The examples of reductions following thelOesrreduction attributable to the use of an amalent invention show afew of the possible temperagamated lead cathode at the low alkalinityunture and current'density values. It is preferred der which this runwas conducted. Example 16 29 to conduct the reductions with thetemperature shows the use of 120 F. as the catholyte temperbetween 80and 110 F. and with the current ature along with a current density of4.0,k the density between 2 to 10. At temperaturesV above product havinga, low P. N. value and a low 110 F. the organic acid and color of theproduct mannitol content and being composed largely of .W are higher andthe product is thereby rendered other hexitols and related materials. ffless desirable for many purposes than one pro- The following example ofa run at ordinary duced at a lower temperature. Further increasestemperature and current density shows the rein current density aregenerally undesirable besults of a low alkalinity reduction (0.5-1.5 g.cause of the increase in power cost andthe fall- NaOI-I per liter ofcatholyte as in Examples 14 l ing off of current efficiency. to 18) withan amalgamated zinc cathode and "U The foregoing 21 examples have beenplotted a glucose concentration of 325 g. per liter of on the graph ofFigure 3, the points represen-ting catholyte. the values of temperatureand grams initial sugar Table V Example Ratio C. D. Temp. P. N. Man.Yield g./dm2/hr. gJamp.

Note that the rate of reduction of Example 18, with an amalgamated leadcathode, is 90% higher than the rate attained in this Example 19 inspite of the fact that the latter run was made 'with an amalgamated zinccathode. It is also vinteresting to observe that substantially the sameP. N. and mannitol content were found in the product of Example 19 aswere found in the products of Examples 14 and 17.

Two further examples follow to show the comparative results in Example20, a run according to the invention, and Example 21, a run at ordinarytemperature and current density. The two examples were lconducted innon-circulated cells, at 325 g. glucose per liter of catholy-te, 20 g.NaOH per liter of catholyte, and with amalgamated zinc cathodes. Thecathodes were corrugated Or scored on their surfaces and the actualactive cathode area was substantially double 'the area of a smooth(plane) cathode `of similar dimensions. The values given for Ratio andC. D. are based on the plane surface areas of the corrugated cathodes.Throughout this speccation and in the claims the term cathode area isused to signify the plane area of the cathode. Reduction was carried toa point at which 90% of the initial glucose had been reduced. v

per ampere being indicated by the respective example numbers.

While glucose was reduced in each of the foregoing examples theinvention is not limited in this respect but may be applied to thereduction of other reducible sugars and mixtures of reducible sugars. ew

It is further to be understood Vas within the concept of this inventionto maintain the conditions of high temperature and current densityeither throughout a reduction or during a substantial part thereof.Moreover, it is not necessary to keep either temperature or currentdensity at a constant value in practicing the invention and desirableeiects and economies can be obtained in many instances by runningcertainparts of a reductionk under different conditions of temperature andcurrent density than the rest of the reduction. p p

Having now described the invention what is claimed is:

1. In the process of electrolytically reducing glucose in a cellprovided with a metalplate cathode and an anode in cathodeand anodecompartpartment, the steps comprisingemployi'ng a soluantenas *1l tionof glucose and an alkali metal electrolyte in Water as the catholytesolution in the cathode compartment oi' the cell, said solutioncontaining from 200 to '700 grams glucose per liter, the ratio of thearea of the cathode of the cell to the volume of said catholyte solutionbeing from 0.25 to square decimeters per liter, passing anfelectriccurrent between said anode and said cathode and through said catholytesolution to reduce the glu- -cosetherein to polyhydric alcohol,maintaining acurrent densityof from `2 to 10 amperes per square.decimeter @surface of said cathodev duringasubstantial part of. thereduction, and simul-- taneouslymaintaining said ,catholyte solution vat,ai-temperature Yof rfrom 80.to 11.0 F.; said current density andcatholyte temperature being correlated;y taking into account the initial.concentrationofglucose in said catholyte, and the ratio of. area of`said cathode to thevolume of catholyte, so that the point dened byplotting the arithmetic value of the temperature in degrees Fahrenheit.as abscissa against `an ordinate which isthe logarithmic value of theexpression wherein Cois-the initial `concentration of glucose in thecatholyte solution in grams per liter R is the ratio of cathode'area tothe volumesof Acatholyte solution insquare decimeters per liter CDis thecurrent density at the cathode in amperes per square decimeter ofcathode surface,

falls within the area ABCDEA in the accompanying graph Figure 3.

2. In the process of electrolytically reducing glucose in a cellprovided with an amalgamated lead cathode and an anode in cathodeand'anode compartments .respectively` separated .by a .diaphragm, andhaving an electrolyte .solution in the 39de vcompartment, the steps.comprising employinga @water solution. of. 20.0 to '700 grams.glucoselpalliter, Sodium sulfaterand from .10 13020 gramsperliter oisodllm. hydroxide. as the catholyte solution in the cathodecompartmentof said cell, .thematic ofthearea offthe cathode of the cellto thavolumeof said catholyte solution being from .-0125, to v10v square.decimeters. per liter, passing .an electr-ic .currentbetweensaidenodeand cathode and through 4'said catholytesoluton to reduce the.glucose therein. to amiXture of polyhydrc. alcholslof.10W- sorbitolcontentr maintaining .a .current density of 2 to 10 ,amperes persquareldecimeter .of surface of said cathode, during asubstantalpart .ofthereduction, andsimultaneously maintaining said catholyteV solution ata temperature of 80 to 110 F.; .saidcurrent density and ...catholytetemperature being correlated, taking into account the initialconcentration .or glucosein thecatholyte and the ratioy of areaofsaidcathode to the Vyolume of catholyte, so. that. the pointdefined byAplotting-.the arithmetic .value ofthe temperature inA degreesFahrenheit`as Vabscissa` againstan. ordinateY which. is; the logarithmicvalue of.the expression wherein Co is the initial concentration of glucose inthecatholyte solution in grams per liter R is the ratio of cathode area tothe volume of v catholyte solution in square decimeters per liter l2 CDis the current-density at the cathode in amperes per square decimeter ofcathode surface,

falls substantially on the line HI in the accompanying graph Figure 3.

3. In the process of electrolytically reducing glucose in a cellprovided with an amalgamated zinc cathode and an anode in anode andcathode compartments respectively separated by a diaphragm, and havingan electrolyte solution in the anode compartment, the steps comprisingemploying a water solution of 260 to 700 grams glucose per liter, sodiumsulfate, and from 0 to 2 grams-per liter of sodium hydroxide as thecatholyte solution in the cathode compartment of said cell, the ratio ofthe area of the cathode of the cell. to the volume of said catholytesolution being from 0.25 to 10 square decimeters per liter, passing anelectric current between said anode and cathode .and through saidcatholyte solution to reduce the glucose therein to a polyhydric alcoholproduct of highl sorbitol content, maintaining a current density of 2 to10 amperes per square decimeter vof surface of said cathode during asubstantialpart of the reduction, and simultaneously maintaining saidcatholyte solution at a temperature of to 110 F.; said current densityand catholyte temperature being correlated, taking into account theinitial concentration of glucose in the catholyte and the ratio of areaoi said cathode to the Volume of catholyte, so that the pointdened .byplotting the arithmetic Value of the temperature in degrees Fahrenheitas abscissa against an ordinate which is the logarithmic value of theexpression wherein,

-Goisthe initial concentration of glucose in the .catholytesolution ingrams per liter R. is the ratio of cathode area to the volume ofcatholyte solution in square decimeters per liter CD isthe currentdensity at the cathode in amperes per square decimeter of cathodesurface,

falls substantially on the line FG in the accompanying graph Figure 3.

4, In the process of electrolytically reducing a reducible sugarselected from the class consisting of monosaccharides and disaccharidesin a cell provided with a metal plate cathode and an anode in cathodeand anode compartments respectively separated by a diaphragm, and havingan electrolyte solution in the anode compartment, the steps comprisingemploying a solution of the reducible sugar and an electrolyte in wateras the catholyte solution in the cathode compartment of said cell, saidsolution containing from 200 to 700 grams of the sugar per liter, theratio oi the area of the cathode of the .cell to the volume of saidcatholyte solution being from 0.25 to .l0 square'decimeters per liter,passing an electric current between said anode and said cathode andthrough said catholyte solution to reduce the sugar therein topolyhydric alcohol, maintaining a current density oi from 2 to 1Gampercs per square decimeter of surface of said cathode during at leasta substantial part of the reduction, and simultaneously maintaining saidcatholyte solution at a temperature of 80 to.110 E.; said ,currentdensity and catholyte temperature being correlated, taking into accountthe initialconcentration of sugar in the catholyte and the ratio of areaof said cathode to the volume of -catholytaso that the point dened byplotting 13 the arithmetic value of the temperature in degreesFahrenheit as abscissa against an ordinate which is the logarithmicvalue of the expression,

falls within the area ABCDEA in the accompany- 15 ing graph Figure 3.

HENRY JERMAIN CREIGHTON. RALPH A. HALES.

14 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 1,612,361 Creighton Dec. 28, 19262,289,189 Hales July 7, 1942 2,289,190 Hales July 7, 1942 2,300,218Hales Oct. 27, 1942 OTHER REFERENCES Transactions of The ElectrochemicalSociety, vol. '75, pp. 289-307 (1939).

Transactions of The Faraday Society, vol. 1'7, pp. 453-456 (1921).

